False flag or not, Putin will try to pin this all on Ukraine to drive military recruiting. So even if it is a failure, it may work to his advantage.

ISIS doing it is the only thing that makes sense.

It's not a Russian false flag because it makes Putin look incompetent.

It's not a Ukrainian op because the US wouldn't give advanced warning, instead they'd tell Ukraine to cut it out.

What we are seeing is a run of the mill ISIS attack followed by misdirection by Putin to shift blame from himself.

My first thought on a false flag was "three days after the election?" Wouldn't you want it before?"

On reflection, no, you wouldn't. The point of that kind of false flag is to make whoever is in power look bad - weak, and in need of a stronger replacement. You don't do that if you are the one in power. Three days after an election gives the maximum time for people to forget about it before the next election.

Then what would be the point? To pin it on Ukraine, to stoke public support for the war.

But I don't buy that, for three reasons. One, from what I gather, they're doing a really clumsy job of pinning it on Ukraine. The data doesn't really support that conclusion. Two, they took too long to blame Ukraine for it. For a real false flag, I would expect the data to point quickly and decisively to the intended fake perpetrator, and only later would niggling questions come out. Third, ISIS is claiming responsibility. (Though groups wanting attention sometimes do claim operations that aren't theirs. Does ISIS do that?)

So overall, I think it's just Putin trying to make lemonade out of lemons, rather than a real false flag. But I'm just a rando posting on the internet, and I don't actually know anything...